Free-cutting aluminum alloys



Patented July 11 1939 -2;l.65,441 FREE-CUTTING ALUMINUM'ALLOYS Adolf .Beck and Hans Bohner, Bitterfeld, Germany, assignors to I. G. Farbenindustrie Aktiengelellschaft, Frankfort-on-the-Main, Germany No Drawing. Application June 19, 1937, Serial No. 149,207, In Germany June 25, 1936 scum (01. 148-211) 1 V This invention relates to a process of rendering aluminum alloys suitable for working with cutting tools.

Aluminum alloys have been proposed which contain, besides at least 3% of magnesium,-addierably within a temperature range extending from tions (to a total extent of 1 to 5%) of one or more alloying components such as manganese, chromium, iron, titanium, vanadium, tungsten,

cobalt and, nickel which form, with the aluminum, hard and brittle inter-metallic compounds' which are practically insoluble in the aluminum.

Further investigations have now. shown that these aluminides primarily crystallising out of the molten alloy, occur mainly as large crystals,

especially when the additions consist of manganese, chromium or iron, singly or in conjunction. It has been found that if such alloys be worked with cutting tools, particularly at high .11

speeds, these-crystals are easily torn out of the structure by the tool steel, so that the worked surface is roughened.

It has now been ascertained, .in accordance i with the present invention,-that a heat treatment (hereinafter referred to as disintegrating heat treatment) at temperatures above 300? C. and preferably between about 400 C. and the eutectic temperature of the alloy (450 C), causes the large primary crystals of hard, inter-m etallic aluminides, by interaction with the surrounding aluminum-magnesium solid solution, or with the aluminum-magnesium-compounds separating out during solidification, to break up into a number of smaller crystals. By-this means, the formation 85 of a rough surface during the working of the ailoy with high speed cutting tools, is-avoided.

Inmany instances it has also been found ad- -vantageous to apply, before orafter the disintegratingheat treatment for breaking down the 40 primary crystals, a further heat treatment (hereinafter referred to as heterogenising heat treat ment) leading to a segregation in the matrix of the alloys, of components previously present in supersaturated solid solution, since the presence 'of the finely divided segregate facilitates the breaking down of the large, primarily separated f aluminides into numerous small crystals. Ob-

yiously howeverthe application of such heterogenising heat treatment presupposes the alloy V to be in a statein which at least part of the AlsMg'z' compound is held in supersaturated solu- ,tion, 1. e. is-of a more or less'homogeneous tex- In order to produce such heterogenisation, the

'55 alloy is subiectedin known manner, to an art-Yv nealing treatment at temperatures below the. boundary line between the a and the a+p fields in'the phase diagram of the binary aluminum- 1 magnesium alloys, but, on the other hand, sumciently high,-i. e. at least about 200 C., and pief- The disintegrating and heterogenising heat 15 treatments above referredto canbe applied in direct succession. In the case'of alloys of .a magnesium content'exceeding about 6%, in which 'eterogenisation may be effected by the application of. temperatures exceeding about 300 C., the 20 disintegrating heat treatment mayieven be combined with the. heterogenising heat treatment, since the application'of one and the same temperature between about 300 C. and the boundary line'separating the.:: from the t -i-p field will 25 produce both effects simultaneously.

If an alloy, which has undergone the disintegrating heat treatment-and in-,.which there fore the primary aluminide crystalsare already present in a broken-down'condition-be subjected, 30

to. plastic deformation, this operation will result in an extensive distribution of the disintegrated crystals of the primary aluminides, so that, after deformation, numerous small aluminide' crystals are present, in a more or less uniform condition 85 ,.'of distribution, in the structure of the alloy. ;When such alloys are worked with cutting tools, the worked areas-exhibit aperfectly smooth surface.

I Owing to the improved distribution, in the 40 structure of the alloy, of the crystals facilitating the formation of cuttings, as the result of the disintegrating heat treatment of the present in- .vention, itis possible substantially. to reduce the amounts of metals, added for the purpose of 45 forming hard, intermetallic compounds, by comparison with those hitherto considered necessary, additions of not less than 0.5% and-not more than 3% beinggsuilicient. By this means, sub- -stantial advantagesare gained, both in the meltto ing process and in all the subsequent treatments. The alloys may also contain up to 10% of one or more of the elements zinc, silicon and copper,

which are absorbed, in the-form of a solid solutiominto the matrix or, in some Example II A structure similar to that described in Example 1 is obtained when an aluminum base alloy containing 9.5% of magnesium, 0.6% of chromium and 0.2% of manganese after casting, solidification and cooling, is annealed for 10 hours at 270 to 300 C. and thereupon subjected to a disintegrating heat treatment for 5 hours at a temperature of from 400 to 420 C.,

and subsequently extruded. In order still further to disintegrate the primary crystalsthe alloy' after being extruded, is subjected to a further heterogenising heat treatment for 1 hour at a temperature of 300 C.

Example III An aluminum base alloy ;containing 10% of magnesium, 0.2% of titanium, 0.35% of chromium and 0.5% of silicon is. subjected to a heat treatment according to either Example I or Example II, and furnished a similar structure favourable for working with cutting tools.

We claim:

1. Process of improving the properties in. re-

spect of working with cutting tools, of aluminum base-alloys containing besides at least about 3% of magnesium a total'quantity of from about 1 to about 5% of at least one metal forming hard intermetallic compounds with aluminum and adapted to react peritectically with the aluminum-magnesium compound formed in such alloys, which process comprises subjecting such alloy in the'solid state to a heat-treatmentwithin the temperature range extending from about 300 C. upwards, until disintegration of the primary crystals of the hard intermetallic compounds has taken place.

2. Process in accordance with claim 1 as applied to alloys containing more than about 6% of magnesium, in which the disintegration treatment is carried out at temperatures below the boundary line separating the aand the +13 field of the aluminum-magnesium alloy phase diagram and is preceded by a homogenising treatment.

3. Process in accordance with claim 1 as applied to alloys containing magnesium in the form of a super-saturated solid solution, in which the disintegrating heat treatment is combined, in the form of a separate step, with a heat-treatment adapted to cause segregation of at least part of the magnesium held in supersaturated solution.

I 4. Process in accordance to claim 1, in which the disintegrating heat treatment is followed by a plastic deformation.

' 5. A process in accordance with claim 1, in which the disintegrating heat-treatment is carried out at temperaturw between about 400 C. and 450 C.

ADOLF BECK. HANS BOHNER. 

